5-MeO-AMT or 5-methoxy-α-methyltryptamine, α,O-Dimethylserotonin (Alpha-O) is a potent psychedelic tryptamine. It is soluble in alcohol.

The sympathomimetic effects may in turn be caused by 5-MeO-AMT's structural similarity to the amphetamines. As noted by Alexander Shulgin, the alpha-methylated tryptamines can be looked at as the tryptamine homologues of the amphetamines (alpha-methylated phenethylamines).

Mechanisms of action such as inhibition of monoamine reuptake may be involved also.

5-MeO-AMT is supposedly sold in 4 mg tablets by the street name Alpha-O and taken as a recreational drug. Since the DEA arrests of the makers of a huge percentage of the United States' LSD in 2000, 5-MeO-AMT may have occasionally been sold under the guise of LSD in liquid, sugar cube, or blotter form, though this may be due to DEA reports of finding it on sugar cubes and blotters "LSD Style".

The most common route of administration for 5-MeO-AMT is orally, however anecdotal reports have stated less common methods such as snorting or smoking. Intravenous (IV) and intramuscular (IM) routes are rarely, if ever, used outside research settings due to the high potency, powerful effects and quicker onset.

Terence Kemp McKenna (November 16, 1946 – April 3, 2000) was an American philosopher, psychonaut, researcher, teacher, lecturer and writer on many subjects, such as human consciousness, language, psychedelic drugs, the evolution of civilizations, the origin and end of the universe, alchemy, and extraterrestrial beings.

Terence McKenna grew up in Paonia, Colorado. He was introduced to geology through his uncle and developed a hobby of solitary fossil hunting in the arroyos near his home. From this he developed a deep artistic and scientific appreciation of nature.

At age 16, McKenna moved to Los Altos, California to live with family friends for a year. He finished high school in Lancaster, CA. In 1963, McKenna was introduced to the literary world of psychedelics through The Doors of Perception and Heaven and Hell by Aldous Huxley and certain issues of The Village Voice that talked about psychedelics.

McKenna claimed that one of his early psychedelic experiences with morning glory seeds showed him "that there was something there worth pursuing." In an audio interview Terence Mckenna claims to have started smoking cannabis regularly during the summer following his 17th birthday.